The present invention relates to a sound volume controller that controls a volume of an audio signal.
When a movie, music, or the like, is played back in the night time, a sound volume (loudnes level of sound) of the audio apparatus is generally set to be low. However, turning down of volume naturally makes a playback of sound hard to hear. In particular, when a movie is played back, turning down of volume makes it difficult to hear a small sound especially, such as words (speech), because the range of volume (a dynamic range) for the movie is wide. In the meantime, when the volume is totally turned up in order to make it easy to catch the words, sound effects and the like, are played back at a high volume level.
In order to solve the problem, there is proposed a sound volume controller that compresses a dynamic range on a per-channel basis; that turns up the volume of words, and the like, to thus make it easy to hear and plays back sound effects, and the like, in a suppressed manner (see; for instance, Patent Document 1).    [Patent Document 1] JP-A-2006-42027
However, according to the configuration of the controller described in Patent Document 1, a coefficient of dynamic range compression is constant at all times. Therefore, depending on a viewing environment there still exists a case where a sound is felt as being too loud or small. In this case, there still exists a necessity for the user to adjust a volume control each time. When dynamic range compression is once set to an active position, a dynamic range is always compressed even in a viewing environment that does not require dynamic range compression as in the daytime, unless the user manually deactivates dynamic range compression.